The therapeutic value of simultaneous application of cold and compression to an injured body part is widely accepted in the medical community, and the acronym RICE for Rest, Ice, Compression, and Elevation, for the primary treatment of injury to joints and limbs of the body, is practiced routinely. After knee surgery, compression and cold are almost universally applied to control the swelling and the commonly occurring hemarthrosis that causes pain and delays rehabilitation. Even so, in a 1983-84 survey by the Committee on Complications of Arthroscopy Association of North America, as published in The Journal of Arthroscopic and Related Surgery, Vol. 1, No. 4, 1985, pp. 214-220, postoperative hemarthrosis was seen in 23.5% of all arthroscopies and identified as the most frequently occurring complication.
Modalities for postoperative cold and compression traditionally have been applied separately--compression most commonly by an elastic bandage wrapped around the knee, and the cold by a superimposed plastic bag filled with ice. While this approach appears simple and economical, it has its own complications. In a 1968 study by Husni, et al., reported in JAMA, Vol. 206, No. 12, Dec. 16, 1968, pp. 2715-2718, it was demonstrated that an ace wrap applied to the knee at a moderate compression of 20 mm hg retards venous circulation and may contribute to thromboembolism. In a 1989 study of various compression dressings, reported in Athletic Training, Winter 1989, pp. 320-323, it was demonstrated that an enormous compression variability existed in the application of an elastic wrap. Four experienced athletic trainers applied wraps to four different ankles four times each. The measured pressures varied from 26 mm to 104 mm hg! While this study was with ankles, it is reasonable to assume that considerable variability must also exist in application of such wraps to the knee.
The risks with this form of compression are suggested by Stringer's 1989 study of "Deep Vein Thrombosis After Elective Knee Surgery", as reported in The Journal of Bone and Joint Surgery, Vol. 71-B, No. 3, May 1989, pp. 492-497. DVT was found in 56% of patients after total knee replacement; in 25% of open menisectomies, and in 4% of arthroscopies. In a 1990 study of "Knee Pressure Dressings and Their Effects on Lower Extremity Venous Capacitance and Venous Outflow", by Normal Mindrebo and K. Donald Shelbourne, publication pending, it was determined that, based on the significant changes in venous outflow and venous capacitance, the routine use of the ace wrap as a postsurgical knee dressing should be discouraged.
Numerous other devices have been introduced in recent years for the application of cold and compression, and studies have demonstrated their relative effectiveness. Sloan, et al., in a 1988 study on "Effects of Cold and Compression on Edema", reported in The Physician and Sports Medicine, Vol. 16, No. 8, August 1988, pp. 116-120, showed that a Cryopac.TM. sleeve that applied cold at 15.degree.-20.degree. C. in a cuff inflated to 30 mm hg by Freon gas was highly effective in reducing edema. It was reported in 1989 in The American Journal of Sports Medicine. Vol. 17, No. 3, pp. 344-349, that using a Hot Ice Thermal Blanket.TM. machine to apply cold continuously at 50.degree. postoperatively to the knee significantly reduced pain medication required by the patients. In 1990 there was reported a similar reduction in pain medication in patients using a DuraKold.TM. dressing consisting of small cells of ice, analogous to a blister pack, in a nylon web support suitable for wrapping around a body part. A 3K Cryotherapy Compression Bandage from Silipos that includes a U-shaped gel filled cooling element in a sleeve that wraps around the entire knee has also been used.
Thus a wide variety of systems have been advanced for the application of compression of cold, and of cold and compression. These include an elastic wrap, the simple ice bag, a freon inflated sleeve, a compressor driven cold water circulating blanket, ice cubes in a strapped-on blanket, and a gel insert in a strapped on sleeve.
But none of these or any other known device has addressed the clearly established need for maximizing the compression and cold in the areas of the knee where needed, while minimizing compression in those areas most sensitive to restriction of venous circulation with its attendant risk of DVT.
This then is the primary object of the present invention. It is to provide a simple and economical device that applies therapeutic cold and a first level of compression to that limited area of the knee that needs the therapy, while using means for controlling the compression below the knee to a second predeterminable amount to minimize the constriction of venous circulation in the lower leg.
To achieve this objective, the present invention includes a cuff with a watertight chamber shaped to envelope only the anterior and sides of the knee, including particularly the suprapatellar pouch. These are the areas where posttrauma body fluids accumulate and where cold and compression are most needed. While the cuff is economically fabricated from sheets of flat material, its novel design permits adjustable shaping so as to conform to the knee even when the knee and cuff are flexed at different angles. The cuff is held in place with an upper proximal strap and a lower distal strap that avoid the popliteal area and minimize constriction. When the cuff is applied to the knee, the straps are secured, but not tightened. Then a first amount of compression is applied to the knee by inflating the cuff to a reasonably predeterminable amount, which causes the chamber to expand. The expansion tensions the straps and applies compression to the areas of the knee under the chamber.
As an important element of the invention, the expansion of the cuff from inflation becomes greater in the area above the patella (where swelling is greatest) and the expansion is restricted in the area below the patella (where swelling is less). This causes the distal strap to be tensioned to a lesser degree than the proximal strap. It is well known medically and tests demonstrate that venous flow is far more sensitive to constriction in the region of the distal strap and less sensitive in the thigh under the proximal strap. Thus, by limiting tightening of the distal strap, little or no pressure is applied below the knee or in back of the knee and constriction of venous flow is further minimized.
The inflation of the cuff can be achieved by either of two means. In the preferred form of the invention, the cuff is strapped in place when empty and is then inflated with ice water which is supplied by a tube from a container that is elevated above the cuff and pressurized by gravity--a method similar to that disclosed as a Gravity Thermal Dilator in U.S. Pat. No. 2,026,747. With this technique the amount of compression is determined by the elevation of the container e.g.,--15"=28 mm hg.
In an alternative form, the cuff is divided into two coextensive chambers. The inner chamber is filled with ice and water before application to the knee. When the cuff is in place and the straps secure (but not tight), the outer chamber is inflated by a hand-held pump or bulb, in a manner somewhat similar to that disclosed in Davis's Thermal Pressure Splint, U.S. Pat. No. 3,548,819. The amount of inflation (and compression on the knee) can then be observed with a pressure indicating device such as that described in commonly assigned copending application Ser. No. 07/502,806, incorporated by reference herein in its entirety, or by the extension bellows type gauge herein disclosed.
The unique effectiveness of the present invention in limiting constriction of venous circulation while applying effective compression to the knee can be demonstrated using a technique similar to pneumatic plethysmography. The lower leg is elevated about 12" above the hip, and a pneumatic cuff is fastened around the calf and inflated to a consistent base-line pressure. Three pneumatic pressure probes are attached to the knee to measure pressure above the patella, under the proximal strap and under the distal strap. A compression dressing such as an ace wrap or the dressing of the present invention is applied to the knee and compressed to a predetermined effective level, such as 28 mm hg. If the dressing constricts venous flow the calf will swell from the trapped blood and pressure in the cuff will rise. Greater swelling means greater venous constriction and greater risk.
In highly repeatable tests it has been found that when an ace bandage is wrapped on the knee to a pressure of 28 mm hg, the calf will swell by about 20 mm hg above base line. But when the dressing of the present invention is applied as specified and inflated with water to the same pressure at the knee, the calf pressure rises insignificantly, by about 2 or 3 mm hg. Thus, the present invention applies little or no pressure below the knee and no pressure in back of the knee.
The reason for this difference can be seen by the pressures measured at the back of the knee under the straps (or at the same location with the ace bandage). With the ace wrap (and all known devices that envelope the knee) the pressures around the knee are generally uniform. Proximal and distal pressures at the back of the leg are the same as above the patella. With the present invention, the pressure under the proximal strap is at one level; however, under the distal strap the pressure is significantly lower, typically only 55% or 60% as high as under the proximal strap and there is no pressure on the popliteal area (the back of the knee).
In an additional test, a cuff was constructed as a complete cylinder completely enveloping the knee, similar to that disclosed by Cryomed. When inflated with water to the same 28 mm hg pressure at the knee, the calf pressure swelled by about 17 mm--an amount comparable to the swelling with an ace wrap, and far greater than with the present novel device.
A further advantage with the invention developed herein is the ease with which compression can be periodically reduced without removing the dressing or adjusting the straps. With the preferred embodiment, the water from the cuff is routinely recycled back to the cooler for rechilling by lowering the cooler below the cuff. During the two minutes or so required for rechilling the water, the pressure in the cuff falls to zero. This permits even any minimal pooling of blood that might occur in the veins to be flushed out. Similarly, in the pneumatically pressurized embodiment the pressure can easily be dropped periodically, without disturbing the straps or rewrapping the dressing, as with conventional devices.
The medical effectiveness of earlier version of the present invention through pre-market clinical trails found that hemarthrosis can be minimized, and pain reduced, by early and extended use of this type of compression dressing. The ideal postoperative knee dressing would improve patient comfort, minimize intra-articular hemarthrosis and have a minimal effect on deep vein hemodynamics.
Thus, it is an important aspect of the present invention to provide a dressing with a watertight chamber for application of pressure and cold to the knee that covers only about the anterior half of the knee, avoids the popliteal area, and is held in place by a pair of adjustable straps at the proximal and distal margin, with means for inflating and thereby expanding the dressing so as to apply compression to the knee after the straps are secured without, or with minimal, tensioning.
The invention also provides means for relatively restricting the expansion of the dressing in the distal area so as to limit tensioning of the distal strap in order to lessen venous constriction. In the preferred embodiment disclosed herein, the restricting means is accomplished by tethering or spot-welding the layers of the dressing watertight chamber in the distal area.
Also, in the preferred embodiment, the novel device has a proximal strap that is inelastic and a distal strap that is elastic to further limit distal constriction.
The invention includes a closed cycle pressurization means that uses chilled water from an elevated container that is connected by a tube to the watertight chamber of the device. By raising the container above the knee, the chilled water pressurizes the device and, when the water is warmed by the body, by lowering the container below the knee, the water is returned from the device to the container for recooling. Alternatively, a compartment of the device may be inflated with air by a novel pump or by a bulb.
The invention is fabricated from sheets of flat material, but the novel design permits adjustable shaping of the invention so as to conform to the knee even when the knee is flexed at different angles.
The novel invention also includes a syphon in the closed chilled water system that permits draining the water from the device without removing the cuff.